錫奈米顆粒的二階段超導相變

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题名:	錫奈米顆粒的二階段超導相變
作者:	蔡昌翰;Tsai,Chang-han
贡献者:	物理學系
关键词:	錫;奈米顆粒;超導;磁性;Sn;nanoparticles;superconductivity;magnetic
日期:	2013-07-29
上传时间:	2013-08-22 11:46:51 (UTC+8)
出版者:	國立中央大學
摘要:	本論文中藉由改變錫奈米顆粒外加磁場及顆粒間距來探討奈米顆粒的超導性以及磁性。本研究使用熱蒸鍍冷凝法製備奈米顆粒，使用X 光粉末繞射(XRD)譜圖及電子顯微鏡(TEM)影像來判定樣品成分與粒徑。經XRD譜圖分析，樣品Sn120318成分為質量65%錫與35%氧化錫所組成，錫奈米顆粒的平均粒徑為16 nm，氧化錫殼層的厚度為5 nm。為了探討錫奈米顆粒的超導性，我們進行一系列的磁化率量測，並利用磁化率隨溫度的變化關係，藉由Scalapino 表示式擬合判定超導參數。我們觀察到在超導溫度時，隨溫度增加，超導抗磁磁化率有兩階段不同斜率的轉變，可使用兩個Scalapino式疊加來描述(χ'=?χ'?_S1+?χ'?_S2 )。藉由改變外加磁場及顆粒間距，發現到兩超導抗磁分量有不同的特性，由實驗結果推測此兩分量可能為錫奈米顆粒的表面超導及核心超導。由磁化強度隨外加磁場的變化量測，也發現了低溫時樣品的超導與磁性共存。在無外加場時，發現有超導抗磁引起磁矩排列；隨外加場超過200 Oe時，有磁場穿透現象。隨壓合密度增加，無外加場時，有自發性磁矩排列。 Sn nanoparticle powders were fabricated by employing thermal evaporation method. X-ray diffraction, transmission electron microscopy (TEM) analysis are used to characterize the powdered samples. The composition of Sn/SnO is analyzed by refining the X-ray diffraction pattern using General Structural Analysis System (GSAS) program. The mass rate of Sn and SnO are 65% and 35%. The mean particle diameters of core Sn and the thickness of shell SnO are 16 nm and 5nm, respectively. In our study, the superconducting diamagnetic screening effect was measured through AC magnetic susceptibility(χ_ac=χ'+iχ''). We observed that the temperature dependence of in-phase component χ′(T) can be described with two of the Scalapino’s expressions combined(χ'=?χ'?_S1+?χ'?_S2 ). It means that there are two superconducting components in the present sample. Then, we applied different magnetic fields and varied the packing fraction of the nanoparticle compact to investigate the effects of magnetic field and inter-particle interaction on the superconducting parameters. The results presented the different superconducting behaviors between the two superconducting components (?χ'?_S1,?χ'?_S2). We attribute these behaviors to the coexistence of surface superconductivity and core superconductivity. The magnetization measurement shows the magnetic behavior of present sample. Below TC, an applied magnetic field clearly reveals the coexistence of superconductivity and ferromagnetic spin polarization. We also found magnetic moment induced in the superconducting state at zero magnetic fields. Above TC, we observed the magnetization sharp increase with packing fraction increase to 20%, at zero magnetic fields.
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